The purposes of the investigation are to study the mechanism of action of the IUD and the prolonged effect of the device on the uterus. Our studies have shown that numerous neutrophils (greater than 5 x 10 to the 5th power) are present in the rat uterus containing an IUD and that an injection of neutrophils into pregnant non IUD-bearing uteri markedly suppresses implantation. Currently we are studying the effects of neutrophils on the metabolism of blastocysts in vitro. In another phase of the proposal the subcellular changes in the corpus luteum of the hamster ovary adjacent to an IUD horn will be compared to that of animals injected with prostaglandin. In another study the relationship between RNA synthesis and the ovarian hormones will be determined in IUD uteri. BIBLIOGRAPHIC REFERENCES: Bartley, C.M. and W.J. Bo. 1976. The effect of the IUD on implantation, ovulation and luteal development in the hamster. Anat. Rec., 184: 353. Bo, W.J., W.A. Krueger, L.E. Sain and P. Cantwell. 1977. The effect of dactinomycin on estrogen-induced uterine glycogen. Proc. Soc. Exper. Biol. and Med., in press.